Operational optimization of large-scale SRF accelerators

Unlike other types of accelerator subsystems, because of the flexibility in setting the gradient in each cavity, an SRF linac has many operational degrees of freedom. The overall linac has an operational envelope (beam voltage and current) that depends on acceptable reliability, cryogenic capacity, and RF power budget. For economic and end-user physics reasons, one typically wants to run as close to the edge of the operational envelope as possible. With about 160 cavities in each of the CEBAF linacs, we have been forced to treat this problem in a very general way, and satisfy other non-fundamental needs as energy lock and rapid recovery from failures. We present a description of the relevant diverse constraints and the solution developed for CEBAF.